Manual FWHM measurements in MaxImDL/CCD confirm the above system evaluation. Visually, the quality of the star images in the corners is undistinguishable from that of stars in the center. Also, I could not detect any chromatic or other effect after the FFC was put in the imaging path. The jury is still out on the effect of the FF200 on star image quality (PSF): one night's testing is not sufficient to evaluate if the excellent tightness of the stars in straight through mode is maintained after the 200FF is introduced.
Conclusion: The above comparison shows that the TEC FF200 does an admirable job on flattening the SBIG STL-11000's field. The APO200FL is now well equipped to face the next generation(s) of even larger CCD chips.
Finally, here is the final result of the M16 image.